1. Field of the Invention
The present invention relates to a display device, and more particularly, to a homeotropic twisted nematic (HTN) mode LCD device that has multiple domains, a wide viewing angle, and a rapid response time by applying photo-alignment to the HTN mode.
2. Discussion of the Related Art
With rapid development of information communication fields, the importance of manufacturing display devices that display desired information is increasing.
A Cathode Ray Tube (CRT) is one of display devices can display various colors and has excellent screen brightness. CRTs have been mainly used for this purpose.
However, with the need for a portable display device having a large sized screen and high resolution, it has been necessary to develop a flat panel display to take the place of CRTs, which have great weight and volume. Such flat panel displays are widely used in monitors for computers, spacecraft, and aircraft.
Examples of flat panel displays include a liquid crystal display (LCD), an electroluminescent display (ELD), a field emission display (FED), and a plasma display panel (PDP).
To obtain an ideal flat panel display, lightweight, high luminance, high efficiency, high resolution, rapid response time, low driving voltage, low power consumption, low cost, and natural color display characteristics are required.
Among these flat panel displays, LCD devices having thin and small sizes have been developed to a point where they can perform as flat panel displays. Therefore, a demand for the LCD devices is consistently increasing.
A related art LCD device will be described in detail with reference to the accompanying drawings.
FIG. 1 is a sectional view showing an alignment direction of a liquid crystal in a mono-domain (single domain) homeotropic twisted nematic (HTN) mode LCD device.
FIG. 2 is a plan view showing the alignment direction of the liquid crystal in the related art mono-domain HTN mode LCD device.
Alignment films 13a and 13b are formed on two glass substrates 11a and 11b, and then the liquid crystal 15 is aligned perpendicular to the glass substrates between the glass substrates.
For reference, FIG. 2 shows the direction of the liquid crystal of upper substrate (an arrow of a solid line) and lower substrate (an arrow of a dotted line) on a panel.
In a general HTN mode, the initial alignment direction of the liquid crystal molecules is perpendicular to the glass substrate. At this time, if an external voltage is applied, the direction of the liquid crystal molecules varies with a direction perpendicular to an electric field induced by the applied voltage, thereby causing a twisted alignment structure in the liquid crystal.
A twist angle does not correspond exactly with an alignment angle. The twist angle can be adjusted according to a concentration of a chiral dopant added to the liquid crystal. However, adjustment of the twist angle is limited by the concentration of the chiral dopant. Accordingly, the viewing angle and color characteristic of the HTN mode LCD device is not better than that of a general twisted nematic (TN) mode LCD device. However, since the initial alignment direction of the liquid crystal molecules is perpendicular to the glass substrates, the rapid response time equivalent to that of a vertical alignment mode (VA mode) can be obtained.
FIG. 3 shows the alignment direction of the liquid crystal in a multi-domain LCD device using UV alignment.
In the multi-domain LCD device, the initial alignment direction of the liquid crystal molecules is parallel to the glass substrates. The alignment direction of an alignment film is adjusted by using ultraviolet rays, thereby obtaining the multi-domain. As shown in the drawing, the alignment directions of the liquid crystal molecules on the upper substrate in two adjacent domains correspond to each other. The alignment directions of the liquid crystal molecules on the lower substrate in two adjacent domains are different from each other. By irradiating UV rays using a mask, multiple domains, such as two domains and four domains, can be obtained. For reference, FIG. 3 shows two domains.
To obtain the alignment direction shown in FIG. 3, the upper and lower substrates are respectively irradiated with UV rays twice.
However, the related art LCD device has the following problems.
First, the mono-domain HTN mode LCD device obtains the rapid response time, however, a wide viewing angle cannot be achieved due to the twist angle of the liquid crystal molecules.
Moreover, the multi-domain LCD device using the UV alignment film can achieve a wide viewing angle, however, the response time is slow, and process steps of irradiating UV rays are repeatedly performed to obtain the multi-domain.